Siding and Trim Best Practice Installation

siding & trim best practice

When it comes to siding and trim the best resource for installation and maintenance information is the installation guide for the product being used.  Proper installation prevents decay, hidden water damage, and extends the life expectancy of the siding.  Siding and trim can be made of many different materials however many of the principals are the same.  In this article we will review the Installation Guide for James Hardie Fiber Cement siding because the illustrations are excellent and these best practice techniques apply to nearly all kinds of siding and trim– See the Quick Reference for Siding and Trim for more information about the most common siding types, potential issues and other considerations.  Even vinyl siding, which is decay resistant, benefits from these best practices as proper flashing and clearances help prevent hidden moisture damage to the framing behind the vinyl siding.  Behind the siding is almost always wood framing and wood framing is vulnerable to decay– for this reason proper installation, flashing and clearances is key to prevent expensive water damage.

Hardie General Installation Requirements
Best practice for Hardie and nearly all other types of siding


Fiber cement siding is known to be a durable product but it can become mushy and deteriorate when exposed to long-term moisture.  For this reason clearances should be maintained from any horizontal surface to prevent it from wicking moisture.  Similar clearances should also be maintained for wood siding, metal siding, vinyl siding and even stucco and masonry veneers.

  • 2″ clearance from roofing (the step flashing should be clearly visible)
  • 8″ from the ground
  • 2″ from hard surfaces like slabs, asphalt and patios
  • 2″ from decks
  • 1/4″ gap between the siding and the flashing


Gutters should be installed in a way that keeps the siding and trim dry to prevent decay over the long-term.

  • Drip edge should always be used to help protect the roof framing and trim from decay.
  • Gutters should never be installed over drip edge flashing.  In some cases flashing may be needed to be installed under the drip edge flashing and over the gutters.
  • Gutters should be spaced 1″ from siding where they terminate into side walls.  Kick-out flashing should be used to help direct water back into the gutters.

Transition Areas

Proper clearances and flashing help prevent leaks and decay where one material transitions into another.

  • Metal flashing should be used at doors, windows, horizontal trim, decking, siding transition areas and block penetrations.  Flashing should also be installed over foundation walls or masonry veneers that extend beyond the plane of the siding.

Pipe/Flue Penetrations

Round pipes, vents and other wall penetrations should be made into a block penetration with a moisture resistant trim and metal flashing to prevent water penetration and decay over the long-term.

  • Block penetrations with metal flashing should be used where pipes and flues penetrate through the siding.

Adhered Masonry

For best practice illustrations for cultured stone see the installation guide by Boral:




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